With constant evolution of radio communication technologies and standards, mobile packet services have been developed tremendously, and data throughput capability of a single terminal is constantly upgrading. Take the Long Term Evolution (referred to as LTE) system for example, a maximum downlink data transmission rate of 100 Mbps is supported in 20 M bandwidth, and in the subsequent LTE Advanced network, the transmission rate of data will be further increased, even up to 1 Gbps.
The user plane data protocol stack of LTE is shown in FIG. 1, the downlink data received by an evolved NodeB (Evolved eNB) from the core network via the GPRS Tunneling Protocol for the user plane (referred to as GTP-U) is unpackaged and sent to the User Equipment (abbreviated to UE) after processed by the packet data convergence protocol (referred to as PDCP) sub-layer, the Radio Link Control (referred to as RLC) protocol sub-layer, the media access control (MAC) protocol sub-layer and the physical (PHY) layer; the uplink data transmission is exactly opposite to the downlink one. The user plane GTP-U data of different services in the connection between the Evolved eNB and the core network are born by the E-UTRAN Radio Access Bearer (referred to as ERAB). The user plane connection between the Evolved eNB and the UE is born by a number of data radio bearers (DRBs).
Currently, the data transmission connection between the network side and the UE is a one-to-one dedicated connection, therefore the signal quality and the size of the used resource of this connection link determines the data transmission performance between the network side and the UE. If the resource used by the link is restricted or the signal quality is relatively poor, the UE's user experience will decrease, which is a great challenge now faced by mobile operators, and although the network capacity extends year by year, it still cannot keep up with the increasing number of user terminals and the increasing user demand on data traffic.
In order to meet the growing demand on data traffic as well as the geographically uneven characteristics of the services, the operators add Low Power Nodes (abbreviated to LPNs), Small Cells or Pico eNBs to increase hotspots in the process of deploying the new generation of communication network (such as the LTE). With the increasing LPN cells, the network deployment environment becomes more complex, meanwhile it also brings some problems. First, because the coverage of a LPN cell is much smaller compared with that of a Macro Cell, the capacity is relatively small, and some LPN cells could easily be fully occupied by users, leading to the load too high, the throughput of the user data is affected, and some other LPN cells or macro cells are at a relatively low level of load. In order to balance the load, the network side needs to perform load balancing operation, but this process is not flexible enough, especially when the number of cells is relatively large, this phenomenon of uneven load becomes more serious because of a lack of flexibility; in addition, because the number of LPN cells is relatively large, when the user equipment, also called terminal, moves within the network, it will lead to frequent inter-cell handovers, causing frequent data service interruption or even call dropped, which causes user data throughput and user experience to decrease. At the same time, this frequent handover results in the terminal and the network, especially the core network, receiving the impacts of a large number of signaling, which may lead to a congestion and even paralysis of system resources.
With the increase of the number of LPN cells deployed by operators and individuals in the future, the abovementioned situation becomes increasingly serious, therefore nowadays many companies and operators are inclined to looking for new enhancing schemes, and Dual Connectivity is one of them. Terminals in the dual connectivity can simultaneously remain connected with at least two network nodes, and for example, the UE remains connected with the macro cell and the LPN cell at the same time. When the network load is not balanced, the network side can adjust the amount of data transmitted by the terminal on both nodes in real time. At the same time, if the UE moves or the LPN cell changes due to other reasons, the other cell can still stay connected, and this change will not lead to the impact of excessive signaling.
However, the abovementioned dual connectivity method currently is only at the demand and demonstration stage, and the abovementioned enhancing scheme is unable to be achieved in the current network structure and process.